Camshaft adjusters are used for a targeted adjustment of the phase position between a camshaft and a crankshaft in an internal combustion engine. They allow an optimized setting of valve timing via the engine load and the engine speed. In this way, fuel consumption and exhaust gas emissions may be significantly reduced and the power of the engine may be increased.
A camshaft adjuster is generally made up of a stator, a rotor positioned in the stator, and two sealing covers. A number of pressure chambers, also referred to as vane chambers, are formed in the stator, and are separated from one another by webs which extend radially inwardly away from the stator wall. Rotor vanes of the rotor which is mounted within the stator engage with the pressure chambers. For adjustment of the camshaft, the pressure chambers are acted on by hydraulic medium, as the result of which the rotor is rotated within the stator.
It is known to provide camshaft adjusters with a locking mechanism which locks the rotor relative to the stator in certain situations, for example when the engine is switched off. For this purpose, it is known to provide locking pins in a rotor which are displaceable in the axial direction and pretensioned in the direction of a locking cover. Due to their pretension, the locking pins engage with locking recesses in the locking cover fixed to the stator, so that the rotor is locked relative to the stator. The locking pins are pushed, against the pretension, from this locking position into a released position with the aid of hydraulic pressure; in the released position, the locking pins are disengaged from the locking cover, and the rotor is not blocked relative to the stator. The action of pressure on the locking pins takes place via a hydraulic channel which is formed in the rotor and which is acted on by hydraulic medium and emptied via an oil borehole. The action and/or relief of pressure in this channel is generally controlled via a switch valve. The volume flow of hydraulic medium is determined by the oil borehole.
It may now be necessary, for example when the motor vehicle engine is switched off, to lock the camshaft adjuster in its corresponding locking position within very short time periods. It is problematic that the locking pin, due to the hydraulic pressure which is reduced only relatively slowly on its high-pressure side as the result of an insufficient volume flow through the oil borehole, is not able to engage with the locking cover, against the pretension which acts against the locking pin, in the required short time.
A rotary vane adjuster is known from DE 199 08 934 A1, including a stator which is driven by the crankshaft, preferably via a traction mechanism and via a drive wheel, and a vane rotor which may be acted on by pressure oil, is in a rotatably fixed connection with the camshaft, and includes means, preferably an axially displaceable fixing pin, for a releasable rotatable fixing of the vane rotor, all components of the rotary vane adjuster which have pressure oil contact being situated in an oil-tight housing.
A hydraulic camshaft adjuster which includes a stator, a rotor, and first and second pressure medium lines is known from DE 10 2005 024 242 A1. At least one pressure chamber is formed between the stator and the rotor, each pressure chamber being divided into two oppositely acting pressure chambers by a vane that is situated or formed on the output element in a rotatably fixed manner. Pressure medium may be supplied to the first pressure chambers and discharged from same with the aid of the first pressure medium lines. Pressure medium may be supplied to the second pressure chambers and discharged from same with the aid of the second pressure medium lines. The camshaft adjuster includes a locking device having a receptacle that is formed on the rotor or the stator, a slot that is formed on the other component, a locking pin situated in the receptacle, and a spring which pushes the locking pin in the direction of the component on which the slot is formed. The locking pin engages with the slot in a defined locking position of the rotor relative to the stator, and may be pushed back into the receptacle by the action of pressure medium on the slot. At least one pressure medium connection is provided between the slot and the pressure chamber or the associated pressure medium line, which are acted on by pressure medium in order to rotate the output element out of the locking position. Each pressure means connection is implemented with the aid of exactly one pressure medium channel. The pressure medium channel is connected on the one hand to the pressure chamber or to the pressure medium line, and on the other hand to the slot. One of the two connections is established in each position of the output element with respect to the drive element. The other connection and the connection between the pressure medium channel and the locking pin are established only when the output element is in the locking position relative to the drive element.